The present investigation was conducted to determine the magnitudes of combining ability and heterosis obtained from hybrids three produced by utilization of CMS, maintainer and restorer lines in rice. The experiment was carried out during the two growing seasons of 2010 and 2011 at Rice Research and Training Center (RRTC) Farm, Sakha, Kafr El-Sheikh, Egypt. Twelve F1 hybrids were obtained from crossing three CMS lines as female parent with four restorer lines. These hybrids were evaluated along with their parents for genotypic variances. The analysis of variance revealed highly significant differences among genotypes, parents, parents vs. crosses for days to heading (day); plant height (cm); panicles plant-1 ; panicle length (cm); filled grains panicle-1 ; spikelets fertility% and grain yield plant-1 except parents vs. crosses for panicle length (cm). The variance among males (testers) were either significant of highly significant for all studied traits. The variances among crosses due to males and females (lines x testers) interactions, showed highly significant SCA effects for all the studied traits except for plant height (cm). The estimated values for variance of general combining ability (σ²GCA) were less than specific combining ability variance (σ²SCA) for all studied traits except plant height (cm). This result indicated the preponderance of non-additive gene action. It was supported by the ratio of (σ²GCA/ σ²SCA) which was less than one for all studied traits except for plant height (cm), indicating that the non-additive type of gene action played a major role in the inheritance of these traits. Heritability estimates in broad sense (h 2 b%) were high for all studied traits. However, heritability estimates in the narrow sense (h 2 n%) were moderate for days to heading (day) (44.58%), plant height (cm) (45.81%) and filled grains panicle-1 (53.80%) and low for the other traits. Three parental lines viz.; IR69625A; G46A and GZ9057-6-1-3-2 were identified as good general combiners for grain yield plant-1 (g). Hybrid combinations as G46A x Giza178; IR69625A x GZ6296-12-1-2-1-1 and Large stigma A x GZ9057-6-1-3-2 showed high mean performances due to the presence of SCA effects.
Combining ability and genetic parameters analysis for agronomic, yield and its component characters were carried out in rice through line x tester analysis of 20 hybrid rice combinations developed by crossing four Photo-Thermosensitive Genic Male Sterility (PTGMS) lines (females) with five male lines / varieties along with parents and check. The 20 hybrids with nine parents were grown in a randomized complete block design with three replications. The experiments were conducted at RRTC in 2010 and 2011growing seasons. Data analysis of variance for combining ability revealed a significant differences among PTGMS lines for plant height, panicle length, panicle weight and filled grains panicle-1 , indicating the importance of additive genetic variance in the inheritance of these characters. The mean squares due to female PTGMS lines were found non-significant for days to heading, tillers plant-1 , spikelet fertility%, 100-grain weight and grain yield characters, indicating the prevalence of non-additive genetic variance and suggesting the importance of heterosis breeding for improvement of rice. An overall appraised of GCA effects revealed that among females; PTGMS-80 and PTGMS-51 had a good general combiners for most characters. Among PTGMS and the tester lines, PTGMS-80 and the tester line JRL-252 had favorable genes for grain yield and the most of desirable characters under study. The hybrid combinations PTGMS-80 x JRL-252 followed by PTGMS-51 x Giza 177 were the best specific hybrid combinations which have significant values for grain yield with desirable characters.
The present investigation was conducted to study the combining ability through L x T design of experiment hybrids for agronomic and yield and its component traits under normal and saline soil conditions. Six CMS lines were crossed with seven restorer lines to produce 42 hybrids where they along with their parental lines were evaluated. The analysis of variance for combining ability revealed highly significant differences among CMS and restorer lines for all agronomic and yield and its studied characters except for grain yield (ton/fed) under both normal and saline soil conditions. Among the CMS lines; Pusa 6A and IR69625A while among the restorers, PR3 and Giza 178R are proved to be good combiners for the majority of the characters including yield, by exhibiting values for high GCA effects. Out of 42 hybrid rice combinations, the top five hybrids based on SCA effects for grain yield characters under saline soil conditions are IR68902A/Giza 182R, IR70368A/Giza 178R, IR69625A/PR2, Pusa 3A/GZ6296R and IR58025A/PR2.
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